[ruby-core:87402] [Ruby trunk Bug#14816] Extension build failure on a system with musl libc

Issue #14816 has been updated by shyouhei (Shyouhei Urabe).


Proposed workaround, not tested though.

```patch
From 01839b509c1bb914337124ac3d1f644b05ef90d8 Mon Sep 17 00:00:00 2001
From: "Urabe, Shyouhei" <[e-mail]>
Date: Tue, 5 Jun 2018 10:26:06 +0900
Subject: [PATCH] C++11 is so bad it introduces a nightmare.

TL;DR see https://developers.redhat.com/blog/2016/02/29/why-cstdlib-is-more-complicated-than-you-might-think/

 - `isnan` is something relatively new.  We need to provide one for
   those systems without it.  However:
 - X/Open defines `int isnan(double)`. Note the `int`.
 - C99 defines `isnan(x)` to be a macro.
 - C++11 nukes them all, undefines all the "masking macro"s, and
   define its own `bool isnan(double)`.  Note the `bool`.
 - In C++, `int isnan(double)` and `bool isnan(double)` are
   incompatible.
 - So the mess.

Signed-off-by: Urabe, Shyouhei <[e-mail]>
---
 include/ruby/missing.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/ruby/missing.h b/include/ruby/missing.h
index dc3fd502b5..8df917498e 100644
--- a/include/ruby/missing.h
+++ b/include/ruby/missing.h
@@ -168,6 +168,8 @@ RUBY_EXTERN const union bytesequence4_or_float rb_nan;
 #    include <ieeefp.h>
 #    endif
 #  define isinf(x) (!finite(x) && !isnan(x))
+#  elsif __cplusplus >= 201103L
+#    include <cmath> // it must include constexpr bool isinf(double);
 #  else
 RUBY_EXTERN int isinf(double);
 #  endif
@@ -176,7 +178,11 @@ RUBY_EXTERN int isinf(double);
 
 #ifndef isnan
 # ifndef HAVE_ISNAN
+#  if __cplusplus >= 201103L
+#    include <cmath> // it must include constexpr bool isnan(double);
+#  else
 RUBY_EXTERN int isnan(double);
+#  endif
 # endif
 #endif
 
-- 
2.17.1

```

----------------------------------------
Bug #14816: Extension build failure on a system with musl libc
https://bugs.ruby-lang.org/issues/14816#change-72386

* Author: akamch (Anatoly Kamchatnov)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.6.0preview2 (2018-05-31 trunk 63539) [x86_64-linux]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
Some extensions fail to build on a Linux with musl (Void Linux). Build of unf_ext is an example. 
isinf() and isnan() are defined as macros in musl: https://git.musl-libc.org/cgit/musl/tree/include/math.h
https://github.com/gliderlabs/docker-alpine/issues/261 "Cannot build native extensions for unf_ext gem" seems to be a related issue.

~~~
$ gem install unf_ext                                                                              
Building native extensions. This could take a while...
ERROR:  Error installing unf_ext:
        ERROR: Failed to build gem native extension.

    current directory: /home/rev/.gem/ruby/2.6.0/gems/unf_ext-0.0.7.5/ext/unf_ext
/home/rev/.rbenv/versions/2.6.0-preview2/bin/ruby -r ./siteconf20180603-29655-wgzu56.rb extconf.rb
checking for -lstdc++... yes
creating Makefile

current directory: /home/rev/.gem/ruby/2.6.0/gems/unf_ext-0.0.7.5/ext/unf_ext
make "DESTDIR=" clean

current directory: /home/rev/.gem/ruby/2.6.0/gems/unf_ext-0.0.7.5/ext/unf_ext
make "DESTDIR="
compiling unf.cc
cc1plus: warning: command line option '-Wimplicit-int' is valid for C/ObjC but not for C++
cc1plus: warning: command line option '-Wdeclaration-after-statement' is valid for C/ObjC but not for C++
cc1plus: warning: command line option '-Wimplicit-function-declaration' is valid for C/ObjC but not for C++
In file included from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/defines.h:153:0,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/ruby.h:29,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby.h:33,
                 from unf.cc:3:
/home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/missing.h:172:29: error: 'int isinf(double)' conflicts with a previous declaration
 RUBY_EXTERN int isinf(double);
                             ^
In file included from /usr/include/c++/7.3/math.h:36:0,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/missing.h:23,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/defines.h:153,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/ruby.h:29,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby.h:33,
                 from unf.cc:3:
/usr/include/c++/7.3/cmath:599:3: note: previous declaration 'constexpr bool std::isinf(double)'
   isinf(double __x)
   ^~~~~
In file included from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/defines.h:153:0,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/ruby.h:29,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby.h:33,
                 from unf.cc:3:
/home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/missing.h:179:29: error: 'int isnan(double)' conflicts with a previous declaration
 RUBY_EXTERN int isnan(double);
                             ^
In file included from /usr/include/c++/7.3/math.h:36:0,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/missing.h:23,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/defines.h:153,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby/ruby.h:29,
                 from /home/rev/.rbenv/versions/2.6.0-preview2/include/ruby-2.6.0/ruby.h:33,
                 from unf.cc:3:
/usr/include/c++/7.3/cmath:626:3: note: previous declaration 'constexpr bool std::isnan(double)'
   isnan(double __x)
   ^~~~~
cc1plus: warning: unrecognized command line option '-Wno-cast-function-type'
cc1plus: warning: unrecognized command line option '-Wno-self-assign'
cc1plus: warning: unrecognized command line option '-Wno-constant-logical-operand'
cc1plus: warning: unrecognized command line option '-Wno-parentheses-equality'
make: *** [Makefile:211: unf.o] Error 1

make failed, exit code 2

~~~



-- 
https://bugs.ruby-lang.org/

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